A stop-limit order will be executed at a specified price, or better after a given stop price has been reached. Once the stop price is reached, the stop-limit order becomes a limit order to buy or sell at the limit price or better.
To enable Stop-Limit Order, in the Exchange interface, choose Settings
Then choose Preferences section
Click on Enable advance order
A notification will display to inform you that by clicking on ENABLE you will be able to use "Market" and "Stop-Limit" orders. Follow the instruction to enable Stop-Limit function.
And you've done!